text:
If I am pushing my aircraft into the hangar with a tow bar, at night, with the engine off, am I required to activate my rotating beacon?
I know there is a similar question here: When to use Beacon, Anti Collision, Strobe, Logo and Navigation lights?, but it doesn't answer my specific question.
Do I need to have my rotating beacon on at night while I park (push) my airplane after I've turned off the engine?
It sounds like an urban legend, but someone told me they heard of someone facing disciplinary action by the FAA due to moving their airplane at night without the rotating beacon turned on, even though they were just pushing it back into the parking spot with the tow bar.
I know the AIM 4-3-23 says

Use of Aircraft Lights
a. Aircraft position lights are required to be lighted on aircraft
  operated on the surface and in flight from sunset to sunrise. In
  addition, aircraft equipped with an anti-collision light system are
  required to operate that light system during all types of operations
  (day and night).

But is pushing an aircraft into parking with the engine stopped (in a non-movement area), considered "all types of operations?"

The lights must be on if the engine is on. If the engine is off, then the lights do not need to be on.

See AC 120-74B, page 12: "Turn on the rotating beacon whenever an engine is running"

The AIM gives good advice, but that is really all it is. It is acceptable methods of complying with the regulations, but you are not required to comply with what the AIM says. In questions of what you are required to do, especially in questions of whether you might be at risk for a violation, we want to look at the regulations in 14 CFR.
14 CFR 91.209 states, in pertinent part:

No person may:
(a) During the period from sunset to sunrise [...]—
(1) Operate an aircraft unless it has lighted position lights;
(2) Park or move an aircraft in, or in dangerous proximity to, a night flight operations area of an airport unless the aircraft—
(i) Is clearly illuminated;
(ii) Has lighted position lights; or
(iii) is in an area that is marked by obstruction lights;
(b) Operate an aircraft that is equipped with an anticollision light system, unless it has lighted anticollision lights. However, the anticollision lights need not be lighted when the pilot-in-command determines that, because of operating conditions, it would be in the interest of safety to turn the lights off.

Note:
Position Lights are commonly called Nav Lights
Anticollision Lights can include what are more commonly called Strobe Lights and Beacon Lights (See AIM 4-3-23)
Lets first look at what the above regulation says about operating requirements. Is your given scenario (engine off, etc.) an example of operating the aircraft? 14 CFR 1.1 gives the following definition of operate:

Operate, with respect to aircraft, means use, cause to use or authorize to use aircraft, for the purpose (except as provided in §91.13 of this chapter) of air navigation including the piloting of aircraft, with or without the right of legal control (as owner, lessee, or otherwise).

By that definition I would argue that towing, pushing, or otherwise moving an unoccupied aircraft with engine(s) shut off would not be operating that aircraft anymore than leaving the aircraft parked overnight would be operating it, since you are not using the aircraft for the purpose of air navigation. Thus I would say that you are not required to follow any rules that pertain to operating the aircraft, such as that any installed anticollision light be lighted.
(This is in contrast to an airliner pushing back with a load of passengers, flight crewmembers at their stations, electrical power on, APU running, etc., which would be operating, since the aircraft is being used.)
This leaves us with the Park or move paragraph. This paragraph specifically pertains to "in, or in dangerous proximity to, a night flight operations area of an airport".
What is a night flight operations area? Absent any proffered definition, the plain reading of the phrase—as I read it—would be an area used, or subject to use, for flight operations at night. In other words, any public use airport with an apron or taxiway that is open to flight operations at night could and should be considered—by my reading—a night flight operations area. Whether the area is a movement or non-movement area shouldn't matter. Could someone else reasonably taxi past you (or into you!) at night? That's probably a night flight operations area.
Thus, for your given scenario, if you are pushing your aircraft back into a tie-down spot on an apron that is open to night flight operations, by regulation it must be either:
a) clearly illuminated;
b) have lighted position lights; or
c) be in an area that is marked by obstruction lights.
I typically see airport ramps clearly illuminated by large overhead lights. This clearly meets the first requirement. Another means of compliance would be to turn on an internal hanger light to clearly illuminate the airplane when you push an airplane in off a taxiway into a hanger.
You are also good to go if you are in an area that is marked by obstruction lights. I don't think I have ever seen these demarcating an area where you would be pushing or towing an airplane (I'm thinking of those lighted construction barriers), but if you saw them I suppose you would know.
In the absence of clear illumination or an area marked by obstruction lights, if you are going to park or move the airplane at night, you had better turn on the position lights. And this, I think, is where you could be at risk for a violation.
Note that, even in that case, the requirement is for position lights, not the beacon. Unless the aircraft is being operated, there is no requirement that any installed anticollision light be lighted.

Great answer, though I think your definition of "night flight operations area" is a little speculative.

@pericynthion You are right. I had used language that made that clear, but I removed it at some point without taking into account that change. I have once again made that clear.

Thanks for this well thought out answer with applicable regs and rationale.

No, pushing or towing an aircraft which is cold and dark is not an activity requiring anti-collision lighting be operative.  The beacon is normally used during aircraft operations where it is powering up and moving under its own power.

Airliners routinely use the rotating beacon during pushback from the gate.

This sounds reasonable, and quoting some sort of regulations would put more weight behind this answer. (don't look at me, I haven't the foggiest idea where to find the appropriate one! IANAP)

@FreeMan AIM 4−3−23. Use of Aircraft Lights
a. Aircraft position lights are required to be lighted on aircraft operated on the surface and in flight from sunset to sunrise. In addition, aircraft equipped with an anti−collision light system are required to operate that light system during all types of operations (day and night).

@JScarry - AIM 4-2-23 was quoted in the OP. He's asking if pushing the plane into a parking space is part of "all types of operations". This answer says it's not and I was suggesting that a regulation reference in support of the answer would help. I'm not implying that the answer is wrong, just that it would be better with a reference.

Actually, further reading of AIM 4-3-23(a) says "Supplementary strobe lights should be turned off on the ground when they adversely affect ground personnel or other pilots..." If you're pushing the plane at night, that strobe or rotating beacon is going to be fairly close to your eyes and may ruin your night vision and/or be painfully bright.

Airliners are also powered up with the APU running; beacon serves as a warning to ground personnel that the aircraft is starting up.

They're talking about wingtip strobes FreeMan or some other lighting capable of distracting or degrading night vision in other flyers.

@MikeSowsun Yes, because during pushback normally the engines are being started or at least the APU is running. As you turn on your anti collision light before you start the APU it is on during pushback.


text:
Is there a difference between how commercial jets and GA aircraft use airways?
In the answer to this question about why people use airways, one of the commentors pointed out that GA aircraft often use airways in a different fashion than commercial aircraft.  I couldn't tell from context why this is true though.  Is it laziness, spite, lack of knowledge?  Or is it simply that GA aircraft are instructed to use them differently?  Or, even, is it that GA aircraft are typically at a lower altitude so they simply have different airways?
Why do GA aircraft use airways different than large commercial planes?

"GA aircraft" covers a lot of ground.  A private pilot out on a VFR cross-country cruise would typically elect to not use airways at all, at least in the US.  Why go where the other traffic is concentrated?

In Europe, some airways are only available in certain flight level ranges, so a commercial airliner and a GA turbo-prop travelling from the same departure airport to the same destination airport could be travelling on different routes due to airway restrictions in place and the inability of one aircraft to climb to the same level as the other. Below the routing for PC12 operating IFR at FL150 and an A320 operating at FL250.
(FPL-DEXAM-IG
-PC12/M-SDE1FGHIJ1RWXY/LB1
-EDDL1000
-N0160F150 KUMIK L603 KOSEK Z74 HAREM T104 ANORA
-EDDM0150 EDQT
-PBN/A1)

The above flightplan from EDDL to EDDM validates for FL240, but anything above FL245 will not pass, it will error out with:
PROF195: KUMIK L603 KOSEK DOES NOT EXIST IN FL RANGE F245..F999
PROF195: KOSEK Z74 HAREM DOES NOT EXIST IN FL RANGE F245..F999
PROF197: RS: EDUUFFM14 EDUUFUL13 EDUUNTM13 EDUUTGO13 EDUUSLN13 EDUUWUR14:F245..F255 IS CLOSED FOR CRUISING REF:[EUROED41A] ED AIP(ENR3.3 1 NOTE 9)

To fly the same flight in higher levels, you would need another routing:
(FPL-DAXAM-IG
-A320/M-SDE1FGHIJ1RWXY/LB1
-EDDL1000
-N0260F270 DODEN Y853 BOMBI T104 ANORA
-EDDM0150 EDQT
-PBN/A1)

This routing works fine for anything above FL245, below it would again error out with:
PROF195: BOMBI T104 HAREM DOES NOT EXIST IN FL RANGE F000..F245
PROF204: RS: TRAFFIC VIA DODEN Y853 BOMBI IS ON FORBIDDEN ROUTE REF:[ED2318A] Y853 DODEN BOMBI
PROF205: RS: TRAFFIC VIA DODEN Y853 BOMBI:F000..F245 IS OFF MANDATORY ROUTE REF:[ED2318B] Y853 DODEN BOMBI
ROUTE135: THE SID LIMIT IS EXCEEDED FOR AERODROME EDDL [EDDL50120A] CONNECTING TO DODEN

As I understand it, Europe has much more stringent routing than in the US, although the routing along the East Coast of the US is also quite stringent.

Yup. I am doing this for fun basically, as I don't hold an IR on my PPL, I only use the proper routing in simulation. When you try doing routes by hand and validating them, you get frustrated after 5min, try another 5min and suddenly get the hang of it. I love it. Jay didn't tag his question with ICAO or FAA, so it's good to have both answers here on his question. :)

instead of a TB20, you should file a PC12 or a TBM-800. the TB20 doesn't have the altitude capability or speed for FL240

I changed it to the PC12. The FP for the GA aircraft is at FL150 N0160F150, I did only remark that the FP would validate up to FL240.

US instrument routes have something similar (but not as complex as Europe): We have low-altitude airways - V (VOR) and T (GPS) - below 18,000 feet MSL, and high-altitude airways - J ("jet routes", based on VORs) and R (GPS) - above 18,000 feet MSL).

It depends on the type of aircraft, and the operational support behind the airplane.
In the Western US (as I would expect is also true for Les Alpes), the terrain is quite high, and there is sparse radio coverage at lower obstacle-clearing altitudes. Lighter aircraft will opt for Federal Airways, which have a Minimum Enroute Altitude that ensures obstacle clearance, and radio navigation aid and voice communications coverage.
Carriers have huge flight operations departments, which plan the routes taken by their aircraft.  Since carriers have scores of flights in the air, they are constantly adjusting routes for traffic and weather, and may file routes that a smaller operator wouldn't consider
For smaller operations, there are "Preferred IFR Routes" published in the A/FD (see below).  They can also obtain one-off or subscription flight operations from companies like Jeppesen, which give them the resources of a large flight operations department.

There are variations in how particular airways are used, but there are not routes that are restricted based on the type of operation here in the US, or anywhere that I know of.
As others have pointed out, there may be various restrictions on an airway (route) such as altitude, times of use, directions of use, etc. but they apply the same to GA aircraft as a commercial aircraft.
Keep in mind that GA encompasses a wide variety of different types of aircraft, including aircraft that have far less and far more capabilities than commercial aircraft.  Saying that a particular airway is restricted to aircraft flying above 18,000 feet does not restrict it to commercial aircraft, and the entire system is based on a first come first serve concept.

With so many of the other answers focusing on lower performance GA aircraft, it's good to see one answer note this is not always the case. Many business jets, in particular, can easily cruise at the speed of an airliner but at even greater altitudes. The Gulfstream G650 comes to mind as an example it matches the speed but beats the service ceiling of your typical airliner by a good 8,000-11,000ft with its 51,000ft service ceiling. Not aware of any current airliner capable of matching that though Concorde could of course top that at 60,000ft when it was in service.

GA encompasses a huge range of aircraft operations, some of which look a lot like airlines and some which don't. For instance, a student at a flight school is very different from a private jet. That said, most GA operations are VFR in small, low, slow planes.
While it varies by country, VFR aircraft are generally not required to file a flight plan nor, in most airspace, even talk to ATC. You can just get in your plane, take off, and for the most part, simply fly wherever you feel like, whether that is sightseeing around town or crossing the country.
Similarly, even if you do talk to ATC, it is a lot easier for ATC to keep planes separated if they're moving at 100kt rather than 500kt. So, they don't need much ability to predict where you're going because they have time to just watch and see.
Also, small aircraft have a much wider range of performance and mission profiles, from training to crop-dusting to pipeline patrol to cross-country flights spread across thousands of small airports, whereas jets are generally all trying to fly at the same optimal altitude for as long as possible between a handful of medium to large airports.
All of these factors combine to result in airline (and to a lesser extent charter jet) operations end up needing a lot more work to keep them from bumping into each other. Airways (and things like SIDs and STARs) help ATC manage that complexity.

"GA aircraft" covers a lot of ground.  A private pilot out on a VFR cross-country cruise would typically elect to not use airways at all, at least in the US.  Why go where the other traffic is concentrated?

Commercial and GA often do use different airways near their respective airports, but when at cruising altitude, you may find GA and small turboprop flying on the same airway, at the same altitude. For example, a small regional Q400 flying from Toronto to Ottawa might be assigned at FL220, and since most GA aircraft are capable of that, it is possible that they can be flying on the same airway, at the same altitude. However, it is a different case when they are near their respective airports. Some GA airports close to large commercial airports have height restrictions and the GA planes are made to follow different airways because of wake turbulence, airway congestion, etc. But lots of times, you can also find GA planes at big airports! For example, Vancouver Intl. has a 2 main runways, and another shorter one for small GA planes.
So basically, GA planes can have different airways, but it depends on the location, altitude, noise abatement procedures, radar capability, airport size, airspace capacity, and many other factors.

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text:
Why is there so much movement of the sidestick during this takeoff?
Watching a video entitled Airbus A330 Takeoff Sidestick View, there appears to be a lot of side-to-side movement of the sidestick, as well as a lot of pushing the nose down:

I was under the impression that movements on the control column should be smooth and not erratic — what is the reason for the side-to-side movement? As far as I can see on the MFDs, there is no heading change prior to 02:50 (which appears to be done by the A/P anyway). Is it turbulence?
Also, what is the reason for pushing the nose down? Is the plane naturally trying to pull up at too high of an angle?
This landing video appears to show even more erratic control. Is this normal?

One of the unique aspects of Airbus fly-by-wire aircraft is that the sidesticks provide NO feedback. Because of this, the planes have an automatic trim system. Once the aircraft is pitched to a desired attitude, the pilot will then release the control stick and the aircraft will continue to fly at the selected attitude.
Correspondingly, if a pilot desires to reduce the pitch, they must push the stick forward to do so. In an Airbus (unlike most other aircraft), a pilot doesn't manipulate trim at all (except in non-normal situations).
As an aside, in the normal flight regime, Airbuses provide automatic protections from unsafe attitudes. Thus, if a pilot desires maximum rate of climb (that is possible in the current configuration), he can simply pull the sidestick all the way back. The computer will automatically keep the aircraft from exceeding maximum load factor and/or critical angle-of-attack.
To answer the other part of your question, the lateral stick movement is likely due to turbulence. Control inputs in large aircraft tend to be more pronounced than smaller aircraft (due to slower aircraft reaction times).

Hmm.. I think alpha floor and alpha max are both related to stalling, not overspeed. Also, maximum rate of climb is not necessarily at the highest angle of attack.

Oops, you're right! That's what I get for writing answers late at night. Alpha protections are specific to stall prevention. I've revised my answer to remove the incorrect information.

For each takeoff in a jet like this, there is a target airspeed that is used during the climb just after takeoff.  When the nose of the aircraft is first lifted, a target pitch setting is used which should get close to that airspeed.  After things start to stabilize, corrections are made to the pitch in order to capture and maintain the desired airspeed.
Pay close attention to the Primary Flight Display during the takeoff:

You will see that the pilot is simply making corrections in order to maintain the desired airspeed and bank angle:

For pitch control (forward and aft stick movement) he is correcting to maintain the airspeed.  If you watch the video carefully, you will notice that each time that the trend vector on the left side of the airspeed line moves up (indicating that the airplane will increase in speed if no changes are made), the pilot pulls back on the stick (and vice-versa) in order to maintain the airspeed.  It looks to me like he is pulling back just as much as pushing forward for most of the initial takeoff, until he starts accelerating just before the 3:00 mark.
For bank control (left and right stick movement) he is correcting to maintain wings level until he starts the turn just before the 3:00 mark.  Watch the yellow triangles at the top of the blue part of the attitude indicator, and you will see that if they don't match up (like in the picture above) that he makes a correction with the stick to line them back up again.

This particular flight must have had turbulence because both the bank and the airspeed were jumping around a fair amount, requiring constant adjustments on the part of the pilot.

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text:
Do any aircraft systems give spoken warnings in a language other than English?
Since pilots are permitted to communicate in their own language to eachother in the cockpit, and to ATC in their own country, it stands to reason that some warning systems like TCAS or TAWS/EGPWS might say "te laag, terrein!"
I've seen some Russian planes with everything written in Russian in the cockpit:

Do any aircraft have systems that give spoken warnings or callouts in languages other than English?
Are any planes built with the option to change the spoken language? E.g. an Airbus talking French?

that looks like a screencap from a simulator...

@ratchetfreak I believe it's a concept aircraft; it was the best image I could find to convey the meaning though. If you can find a nice hi-res image of a Russian cockpit with their labels clearly visible, please edit it!

I'm almost positive I've heard of an Airbus speaking French, but I haven't been able to confirm that...

I would expect that planes mainly in use in the chinese and russian market are sold with options for "native" languages...

I doubt planes will speak at all ;)

This reminds me of Firefox.

@DannyBeckett Why does one need an image to convey the concept of a cockpit that's labelled in Russian?

@DavidRicherby sadly a lot of people are so US centric that they simply won't believe anything non-American exists...

There's a pretty nice photograph of a Tu-144 panel on Wikipedia, where you can fairly clearly see that everything is written in Russian. I can't imagine that if this aircraft had automated spoken audio, that it would be in any language other than Russian.

@voretaq7 "I'm almost positive I've heard of an Airbus speaking French, but I haven't been able to confirm that..." I believe it's speaking English with a French accent... "retard ... retard ... retard" :)

The L-39 I flew had Russian labels and Russian nav /comms. The important ones had placards over them in English.

I am quite sure that the systems that provide audio warnings for commercial aircraft, such as enhanced ground proximity warning computers, provide English Only. I am pretty sure because on the wiring diagrams there are no kind of dip-switches for language selection and for loadable software it is tightly regulated without any 'language selection' options.  One could imagine that separate part numbers are created for different languages but I know this is also not case case as international carriers share/pool spare black boxes. Basically aviation language is English.
I also see no future provision for other languages as it was only recently in 2008 that ICAO mandated English for all international flights (Amendment 164 to Annex 1 ). Under this ruling Air Traffic Controllers and Flight Crew Members engaged in or in contact with international flights must be proficient in the English language as a general spoken medium.
Regarding Airbus (and the love that the French have of their language) we might do well to know that actual official language of the Airbus company is surprisingly to some 'English.'
Of course I can't comment on military applications much. Actually, I was previously slightly involved in supporting a military aircraft and from what I can tell they use many modified versions of the same components commercial aircraft do. At least for US, British or French allies, who are allowed to import the technology. However, they are modified directly by the customer to be more security tolerant. For example, a military aircraft might not be transmitting its location around the globe unless the receiver has a decoding ability to a secure military key. So even in the small exposure I have encountered with military applications, I have not encountered or heard of 'language options.'  This is not to say that some Chinese or Russian might be heard in some remote aviation system somewhere but that if it does outside their aerospace industries it must be rare and still a 'one language' only feature. Possibly there are missile guidance systems in Russian, Chinese, or Korean but certainly not in international commercial aviation.

This answer seems to mostly assume that the whole world is Europe and the USA. Russia and China build a lot of aircraft, both civilian and military. I for one would be surprised if the non-export versions of those aircraft give spoken warnings in English. A possible contributing factor to the crash of CrossAir 498 was that Russian artificial horizons work in the opposite way to Western ones. That's one example of Russia not following Western conventions; why should we assume it follows others?

@DavidRicherby - Yes. I am really only answering the narrower question (i.e. major aerospace suppliers to actual international carriers). This is really part 2, of this very wide open original entitled question.


text:
What is the possibility of a depressurization emergency during a commercial flight where all or some of the oxygen masks fail?
Can we calculate this? Or is it almost impossible?

http://stats.stackexchange.com/

For the case "all masks", a pressure sensor triggers the masks release when the cabin equivalent-altitude is more than 14,000 ft. If it fails, the crew is informed and can override it

The oxygen system for passengers in an airliner is generally powered by a chemical oxygen generator.
The generator contains chemicals, which when they come into contact with each other, commence a reaction that produces oxygen for a few minutes.
The act of pulling down the mask triggers the contact between the chemicals.
A generator typically serves two or three seats, and each generator is independent of the others on the aircraft. They are not part of a single system with common points of failure.
The panel behind which the masks is opened by a pressure switch, and can also be opened manually.
However the crew will use bottles of oxygen, and the flight crew will use a more complex system that also includes smoke hoods.
Conceivably (anything is possible) a manufacturing fault or sabotage could render every single one of the generator/mask sets inoperative, but it would be an extraordinarily unlikely thing to happen.
People often imagine a system of pipes carrying oxygen to all the masks, but in fact such a system is rarely used. One notable example is the earlier (-100 to -400) variants of the Boeing 747, in which the oxygen is indeed piped. And, apparently, may have not always worked as expected:

The flight crew donned their oxygen masks and manually deployed the passenger oxygen masks.
[...] The PIC was also advised that there appeared to be no oxygen flowing through any of the passenger cabin oxygen masks, however this did not seem to have had any ill effect on the passengers. After the PIC cycled the passenger oxygen switch, a momentary surge of oxygen through the passenger masks was observed.

(from an Australian Transport Safety Bureau report into a November 2001 incident)

The 747-100 through -400 models used oxygen canisters and piping for the passenger oxygen system rather than chemical oxygen generators. I don't know about the 747-8

@TomMcW thanks I have updated the answer.


text:
Why do aircraft have two brake pedals instead of one?
Why do aircraft have two brake pedals instead of one?  If each pedal controls different sets of wheels e.g. the left wheels and the right wheels of the main gear, is that not a safety flaw given that at any point in time, it is impossible for the pilot to apply an equal amount of pressure to the brakes?
Isn't ABS enough to the point that only one pedal is enough?
Finally do both captain and pilot step on the brakes at landing? If not then why have two pedals?

Related: What is differential braking?

The control yoke in front of the pilot is not a steering wheel, many aircraft the only way to steer it is to step on the right or left brake to make it turn...

There is indeed a learning "curve"!

Very few aircraft have ABS, most are flown by a single pilot.  You also don't usually want to apply equal force to both sides: you apply whatever force is needed in order to get the plane to go where you want it to go.

Some airplanes don't have any brake pedals.  A Yak52, for example, has a hand operated air brake with differential braking selected by the rudder pedals.

tractors also have dual brakes, and for the exact same reason, tighter turns.

@hildred: Likewise tracked & skid-steer vehicles.  That's the only way they can turn, either by differential braking or application of power.

There is a feedback loop, when pressing the pedals you observe what happens and modulate the pressure to each pedal accordingly, the same as braking in a car, just with two pedals instead of one.

I'd just like to comment on it is impossible for the pilot to apply an equal amount of pressure. Surely this mechanism has been in use since before many of us are born so it must work. A lot of tanks also work this way: two throttle/clutch levers instead of a steering wheel one for each track. And tanks can still travel in a straight line even though it's impossible to apply same amount of force to both levers. How does this work? The pilot/driver constantly make small unnoticeable corrections (same as when you drive a car or ride a bike). It turns out humans are excellent control computers

In an aircraft the brake pedals control the respective side brakes. This allows for the pilot to turn the aircraft not only with the pivoting nose wheel (if it has one) but also with the brakes. This allows for a very tight turning radius.

(source)

If each pedals controls different sets of wheels eg the left wheels
  and the right wheels of the main gear, is that not a safety flaw
  rather than measure given that at any point in time,

It is by design to allow for the tight turning. Some smaller aircraft also do not have a steerable nose wheel so differential braking is the only option.

it is impossible for the pilot to apply an equal amount of pressure to
  the brakes?

Pushing equally on each toe pedal will result in equal brake operation.

Isn't ABS enough to the point that only one pedal is enough.

The pedals allow for brake steering which a single pedal would prevent. Airplanes also do have ABS but that simply prevents the tires from skidding.

Finally do both captain and pilot step on the brakes at landing. IF
  not then why have two pedals?

Im not sure, when I fly with an instructor or co-pilot in smaller planes only one person operates the brakes.

I find your spellings of "break" and "peddle" very funny (sorry couldn't resist).

Can't differential braking overload the nose wheel if the wheel is not steerable?

@Ruslan, when the nose wheel (or tail wheel) is not steerable, it is free castering (similar to wheels on an office chair or shopping cart).

@kevin - I make that mistake all the time, I'm glad someone else sees the humor in it.

@Ruslan generally no, the nose wheel is often castering as Jan Hudec mentions. Im not sure there are any big planes that have them but lots of small GA planes do

Also in many (maybe most) light planes that have a steerable nose or tail wheel, the steering is linked to the rudder/brake pedals.  Also note that those pedal assemblies control the rudder as well.

@Dave The B-29 had a castering nosewheel.

@MatthewGauthier, I know some big military planes did I belive some even had castering mains to allow for cross wind landings without the longitudinal axis of the aircraft in line with the runway.

Tailwheel aircraft are pretty much impossible to steer on the ground without the ability to brake on one side and not the other.  At speed on the ground the steerable tailwheel and propwash over the rudder allow small changes of direction, but to make sharp turns when taxi-ing, you need to be able to press one brake and not the other.

@Flynn: Why is a steerable tailwheel on taildraggers so much less effective than a steerable nosewheel on tricycle-geared aircraft?

The left pedal is for brake(s) on the left side of the aircraft only, and likewise the right pedal for the right side.
We use two pedals because it is common where differential braking are applied, in other words different amount of braking on the two sides of the aircraft.
This is handy for maneuvering the aircraft around corners. For example if the plane needs to be turned to the left 90 degrees to enter a taxiway, and the length of the fuselage is long, applying left brake during the turn can reduce the turn radius, making it possible to turn without the outer set of wheels running onto the grass.
During a normal landing rollout, equal amount of pressure is applied to both pedals. The difference between both pedals caused by human application is minimal and does not have an observable effect.
Usually, only the pilot flying would be operating the controls, therefore only the pilot flying would apply the brake pedals. Except in an emergency where stopping distance is critical, the pilot monitoring may apply pressure to his own pedals to ensure maximum braking is achieved.

Note also, the pedals are used to swing the rudder to the right and left, to yaw the aircraft, so two pedals are already there. It then makes perfect sense to split the brakes for all the above reasons.

One part of the question was If not then why have two pedals?. This answers it.

To add to the correct answer: two brake pedals allow for differential braking to steer the aircraft when it is on the ground
In light planes, differential braking eliminates the need for a steerable nose wheel. Instead, the nose gear simply casters, rotates as differential braking alters the path of the aircraft while in taxi. This makes for a much simpler and lighter nose wheel, plus no linkage to a wheel in the cockpit. With aircraft, simple is good. Simple doesn't go wrong as often as complex.
In heavy aircraft that usually have a steerable nose wheel, differential braking takes a lot of stress off of the nose wheel. Steering a heavy aircraft with the nose wheel alone puts a lot of angular stress on it. Heavy aircraft are, well, heavy. If all steering was done with the nose wheel, it would need to be beefed up to handle that, on top of being retractable. Differential braking on a heavy aircraft makes for a lighter nose gear arrangement.


text:
How can the runway allocation process be optimised?
I would like to write a programme that would be able to find the optimal arrival sequence for a given list of aircraft on a given airport.
By optimal I mean in terms of delay, fuel burn and runway throughput
Before this, I'm trying to collect information on the matter because I'm totally novice. I have a few questions
Do air traffic controlers only use the First Come First Served (FCFS) principle to assign runways to aircraft or are there other algorithms ?
I've read that this principle can prove inefficient because, for example, it doesn't consider aircraft "size". I've read that a sequence of 5 small aircraft followed by 5 large is better than one alternating 10 large and small aircraft because less spacing required. Is it true ?
Do you have other examples showing that the FCFS is not optimal ?
When is a runway allocated to an aircraft ? When it reaches the Initial Approach Fix ?
Thanks a lot for your help!
Sorry for the mistakes, english is not my native tongue

This is not an easy (or short) answer. Runways are not always allocated on "first come first served", or by initial approach fix. VFR aircraft don't go to the IAF, so they would never get sequenced. Often faster aircraft are vectored in while slower aircraft are on long finals. This depends also on the type of traffic into/out of the airport. Aircraft in distress can override all other aircraft, medivacs, etc.

This should get you started http://www.skybrary.aero/index.php/Arrival_Manager_(AMAN)

Thank you for your answers, what is the scope of an arrival manager ? I mean, I don't really understand at what moment it allocates the aircraft a position in the sequence. Because I guess there is a minimum preparation time required before landing. Also, I often hear about holding stacks, but where are they located ? Near the point where the aircraft is given a position in the sequence, so if it has to wait it doesn't have to go to another location ?

This question is extremely broad. At airports where there's multiple runways, there are numerous factors influencing which aircraft get which runway. Factors include, noise sensitive areas(so one runway should be favored over others), runway length/operational necessity, and configuration.
When an airport has multiple runways usually the tower will decide which are being advertised as arrival/departure runways. At which point the approach control will sequence to those given all the restrictions. Runway assignment usually occurs upon the aircraft entering the approach control's airspace. Once assigned to a runway, it's up to the controller to decide on the sequence, factors include airspeed, distance, and somewhat weight category. If you have multiple heavies coming in, it's often better to group them, than mix small-heavy, BUT you need to have the volume to be able to setup that kind of mix, to minimize space.

Thank you for your answer, just one question : what do you mean by "volume" ?

Number of aircraft over a given amount of time. There's various numbers for how many aircraft a runway can absorb in a given time frame, due to conditions of what approach and aircraft mix.


text:
Are there laws about how close military aircraft can fly to passenger jets, and are they enforced?
Yesterday I was on a passenger plane flying at 35000 feet from Denver to JFK on a fairly clear day. Just west of Sioux City, we made a relatively sharp, but short, right turn for whatever reason (may be unrelated). I happened to be looking out my window and caught what appeared to be a military fighter jet (presumably from the Air Force base there) flying in the opposite direction. It blew past my field of vision in a fraction of a second, slightly below us and off to the right, close and fast enough to startle me. It left a beautiful set of trails but, while my distance judgments aren't very good from a plane, appeared to be no more than ~1000 feet away from us (based on its size, I imagined it to be about 4-5 NYC city blocks away, that's my only reference). The passing aircraft's trails were dead straight at least as far back as they extended before dissipating. I didn't get a chance to ask the pilot about it after the flight.
My only knowledge of separation laws is from wikipedia, which seems to state a 2000 foot limit above 29000 feet.  I absolutely might be misjudging distance, but this aircraft seemed to be well under a half a mile away. So my question is: Are there a different set of separation laws for military aircraft, or perhaps are existing laws just not as strictly followed / enforced by the military? Would the pilot of one of the aircraft expect some sort of reprimand later? Was this a normal occurrence or was it a close call?

This is somewhat speculation, but here's what I think happened:
You were flying at around 35,000 feet, in RSVSM airspace. The fighter jet was correctly on track 1000 feet below you. Without any other guides of distance, you tried to judge its distance by apparent size compared to real size. You might have underestimated the size of a fighter jet; they're typically about 50 feet long. I know I, for one, always thought they were much smaller. Thus what looked like "slightly below" was actually 1000 feet below you.
As for the more general question you posted: the military can get as close to other aircraft as they damn well please, through a procedure called Military Assumes Responsibility for Seperation of Aircraft, or MARSA (thanks to fooot for pointing this out!). Generally this only happens with a civilian aircraft during an interception. I don't know the specific procedures that are followed, but I know that in the past intercepting pilots have gotten close enough to pick out individuals in the cockpit.
As for enforcement, the question is kind of null. Generally, if civilian pilots violate separation without putting anyone in danger, the air traffic controller will just yell at them for a bit, but it does depend on the case. The FAA doesn't have much authority over the military, however. If the air traffic controller passed the information on to the military, perhaps there could be some sort of corrective action, but at this point I'm just guessing.

Military aircraft can follow what is called MARSA, where the military assumes the responsibility for separation of the aircraft (rather than ATC). This can be between two military aircraft (formation flight) or with a civilian plane (interception).

@fooot ah, thanks! I thought that was just between military aircraft. I'll edit that in.

Thanks. As for the jet I saw - I bet I underestimated the jet's size; I also didn't realize they were that big (even looking at pictures of them it's hard to believe they're in the 50 ft range)... Looking at a 5-story building from 5 blocks away now, the aircraft definitely appeared a bit smaller than that; possibly up to 2000 or more feet away, which is pretty unremarkable. It was a little less than 45 degrees down and to the right - more right than down.

@raptortech97 - ATC violations are quite serious in the military as well - stuff like deviating from clearances and breaking rules, unless you have good reason, can make you lose your wings in a heartbeat

Wow, heh, I stumbled on this video by accident today, reminded me of this post.


text:
When should the half bank mode of an autopilot be used?
Half bank can make turns more comfortable for passengers, but ATC expects turns to be at standard rate much (most?) of the time.  When is it permissible to use half bank?

Seems like the accepted practice is to use half rate when faster than 250 knots, in cruise, or when flying in icing conditions.
The AIM (5-10-3) also states that pilots should use half standard rate (through probably referring to hand-flying) when on final of a no-gyro approach like a PAR.
The rest of the time, in terminal areas and when holding, standard rate is expected by ATC. When unable to maintain standard rate (icing, for example) in those cases, notifying ATC should suffice.

Is there any reference that says that 1/2 bank is permissible when faster than 250 knots, or in cruise flight?

The FAA Instrument Procedures Handbook page 5-39 mentions this: "Unless a holding pattern or
teardrop procedure is published, the point where
pilots begin the turn and the type and rate of turn are
optional."  That's basically the only FAA citation I can find. It sounds like the FAA only expects rate 1 during holding.


text:
Should ADS-B airborne and surface squitter transponder registers both be updated regards air/ground status?
ADS-B have two position squitters, airborne and surface. As far as i know, airborne position is broadcasted on air and surface position broadcasted on ground.
There is a "Squitter Capability Subfield" in BDS Register 10, which needs to be set if both airborne and surface position registers are updated within last 10 seconds. This kinda implies both registers shall be updated all the times.
Is providing data for both squitters necessary regardless of aircraft's vertical status? Can we select one of these squitters and provide data only for it?

I don't have the 1090ES MOPS at hand here, but it makes sense to me that both should be updated.
At the moment that the registers are updated, it is not necessarily clear whether an airborne or a surface squitter will be transmitted next. In the period between update of the register and transmission of its contents, the vertical status of the aircraft can change.

You are correct.  Part of it is the independence of the update and the squitter. The other is the need for the extrapolation/estimation of the position data to coincide with the 200 msec epoch.  If you're not constantly "feeding" the extrapolation algorithm by updating the fields, the position data either won't be available or won't comply with the time of applicability.


text:
Are ADS-B Airborne Squitters inherently inaccurate?
Right now I am reading related passages/sections from ICAO Annex 10 Volume 4 and Technical provisions for Mode S Extended squitter.
Airborne position squitters are randomly distributed in between 0.4 and 0.6 seconds. Even if we update Airborne Position Register 05 with utc-synced estimated position, transponder's choice of transmit time might cause in shifting into next epoch(basicly 0.2 second lag).
Increasing rate of update(5hz suggested for now) might only reduce the problem.
Are ADS-B Airborne position squitters inherently inaccurate?

Yes, there is a inherently inaccuracy caused by the delay between a position is determined by the GPS receiver and the time it is transmitted.
However, for installation certified for the EU and USA ADS-B regulations, the inaccuracy is very limited. The accuracy of ADS-B is therefor better than radar even when ignoring the latency in radar systems.

The first part of the latency is caused in the GPS unit itself; there is some processing time between the position signals arrive at the GPS antenna and the  of the time of output of the computed position. Further delay can occur if the GPS-receiver is not directly wired to the transponder. If the position signal has to travel through another box (for example the ADIRU) additional latency can occur.
Finally the position arrives in the transponder and is delayed until the next position message is scheduled for transmission.
In installations certified for the ADS-B mandates of the EU and the USA, the position latency is limited to 0.6 seconds. This is usually achieved by direct wiring the GPS to the transponder. Additionally the latency is compensated for by extrapolating the position using the ground speed vector. The position within the transponder is thus update periodically (e.g. at 10 Hz) using the groundspeed vector. This extrapolation reduces the effect of latency by introducing a small error based on the accuracy of the groundspeed vector and any manoeuvring going on.
The total accuracy of the ADS-B signal is the combination of

GPS accuracy
accuracy of speed vector used in the latency compensation
manoeuvring going on between the time of position validity and time of transmission not compensated for by the linear extrapolation using the speed vector
residual uncompensated latency

In some installations the residual uncompensated latency is negative (i.e. the position is over-extrapolated). The limit is 0.2 seconds ahead of the current position. The recommendation in the ADS-B Minimum Operational Performance Standard (MOPS) is that the uncompensated latency should not be more than 0.4 seconds.
Note that most of the inaccuracy due to latency is only observable in the along-track direction.
The magnitude of the position error caused by the latency is very limited.
For an aircraft flying 270 meter per second (972 km/h, 525 KTAS), the upper bound of 0.6 seconds latency limits the error to 162 meter. That is much better than the position accuracy that en-route radars typically achieve (and in addition, radar also has latency).
In the TMA, the speeds are usually slower and so are the latency induced errors. So ADS-B here outperforms the TMA radars.

For reference, the 0.6 seconds is a limitation in the USA is from FAA AC20-165A (PDF) and in the EU from EU 1207/2011 (applicability dates amended by EU 1028/2014). The full Certification Specifications for ADS-B in the European Union can be found in the CS-ACNS.

Thank you for such complete answer and contribution to online information database for ads-b. I was trying to reduce inaccuracy by taking gps to transponder latency into account for extrapolating position, thus trying better position estimation at the time of ads-b signal reception by ads-b in systems. Can you also point me to the 0.5 second limit for position, maybe an icao certified document.


text:
Do only 0.3% of U.S. air force applicants become fighter pilots?
Here, it says only 3 out of 1000 that apply become fighter pilots. Is this statistic true? (It seems like a very low percentage)
If so what is the main difference between the 3 compared to the remaining 997? What did the 3 do differently than the 997?
(I know that the answer probably is it depends, but what are they looking for when selecting pilots?)

Out of 1,000 what?  A thousand people who looked up at an airshow and thought "wow, cool!" -- maybe so.  Per thousand 2Lt's who start pilot training? Not even remotely.  That article isn't quite garbage, but it's pretty close. I certainly wouldn't take their statistics as gospel.  After all, 87.23% of all stats are made up on the spot!

Also highly relevant, given a quick look at https://en.wikipedia.org/wiki/List_of_active_United_States_Air_Force_aircraft suggests that an USAF is between 10 and 25% fighter aircraft depending how you count them, and not all pilots are in flying positions. So at even given time 'fighter pilot' will be only a subset of current USAF pilots, but a larger % will be qualified to fly them.

Some older numbers for a different airforce here are probably still relevant in talking through the odds.
An airforce has fairly fixed need for number of active pilots, driven by the number of airframes. Many of those airframes are not in fact fighters, so many serving pilots are not fighter pilots.
The profession 'pilot' is one that many people think they understand, and can see themselves doing so more people will walk into a recruiting office with idea of being a pilot than say 'network technician' or 'Airborne Electronics Analyst'*.
Fighter pilot is a specifically demanding profession that requires a high degree of physical fitness, aviation, technical and tactical knowledge and ability to apply all of those under pressure where consequences of being wrong can be highly lethal.
These factors combine to mean that a military will happily let large numbers of applicants put 'pilot' at the top of their preferences form and then based on skills or lack thereof found during testing and assessment filter them into ground support, flying non pilot , pilot of non fighter aircraft and hopefully get enough actually qualified fighter pilots left over.
So a high percentage of people who show up at the recruiting tent and taking the 'how to become a fighter pilot' brochure NOT becoming fighter pilots is the system largely working efficiently from the military perspective (would be better if people showed up WANTING to become more obscure professions of course).
If you are in the position where this number matters directly to your career goals, what matters far more is the % of actually fully qualified candidates not making the cut for the current cycle, rather than % of people who the system will route into other professions.
*at time of writing listed as a priority recruiting position (faster processing and less competition) and at a higher starting salary than pilot.

Somewhere I read an article about a European country-- Sweden maybe? -- where they do things differently and the percentage of candidates entering the flight training program who get "washed out" is dramatically lower than elsewhere.  (Don't recall exactly what the article said about the fighter pilot track though-- that may be highly selective, with those not qualifying being diverted to transports etc?)

@quietflyer, certainly it is mildly deceptive to sign people up up for the pilot dream and then switch them into another profession once committed so a fairer process is certainly possible. Equally if older figher pilots define the process they may like a high washout rate because the survivors can feel 'elite', while a process setup in more civilian lines will try to only spend time on valid candidates and having spent that time be less prone to 'one mistake and out' testing.

Partial "answer" here, based purely on anecdotal experience.
This answer addresses the OP's question "If so what is the main difference between the 3 compared to the remaining 997? What did the 3 do differently than the 997?" It is based on personal observations and opinion more than anything else.
Back in the day (1982), I attended United States Air Force Undergraduate Pilot Training (UPT). On day one, there were 50 highly qualified candidates. The washout rate over the year-long course was such that only 25 of us were ultimately awarded pilot wings. IIRC, about 12 of us were deemed qualified for fighter assignments.
Over the years, I've come to conclude that the primary trait separating the graduating 25 from the washed-out 25 was the ability to learn new things quickly. I have always believed that, given enough time, our flight instructors could have made Air Force pilots of almost all of the washouts, if given enough time. However, the Air Force allowed only one year. In their defense, they could afford to be picky, since the supply of "wannabees" seemed endless at the time...

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What would an all-flying aileron look like, and would it be a good idea?
The only info I could find about someone doing this IRL was the British Army Aerorplane No. 1, but I don't think it ever flew with them. I don't know much about how this would affect the aerodynamics, but maybe it would give more roll? I'm not that experienced in aviation, could someone tell me the implications of this?

See https://aviation.stackexchange.com/q/46195/38119.   The Spratt Controlwing seems to be the best example of changing each wing aoa individually.

None of the answers to date have mentioned the aileron design of the Kitfox, which trails a few inches behind and below the trailing edge of the main wing.  Is that more or less what you had in mind?

The word aileron specifically refers to a part of the airplane, usually, but not always, connected to the back edge of the wing, that is used to control roll and to turn the aircraft when used in conjunction with the rudder.

The British Army No. 1 was based on the Wright Flyer design, and while some early airplanes did incorporate wing-warping to bend the wing itself instead of using ailerons, the No. 1 actually incorporated separate ailerons, mounted above and in front of the leading edge of the lower wing.

Perhaps, instead of aileron, you meant to say wing or airfoil. In that case, several examples exist of modern flying-wing aircraft, such as this B-2 Spirit, which designs the entire aircraft as one large airfoil.

UPDATE
Wing-tip ailerons were utilized in some designs, such as this Stout Skycar.

NASA did testing on this aileron configuration to determine whether or not this design would counteract the adverse yaw effect of traditional aileron placement. When ailerons are behind a wing with a large upper camber, it can partially shield the aileron that is deflected up, reducing its effectiveness. Moving the ailerons to the wingtips proved to significantly mitigate this issue, although not entirely - this due to the interference between the outer edge of the wing and the inner edge of the tip aileron. Nevertheless, there were also significant problems. The NASA study showed a substantially reduced rate of climb compared to traditional trailing-edge aileron. Additionally, there was a near doubling of drag from each wing, largely due to vortex generation caused by the necessary gap between tip aileron and wing. Further, while a traditional aileron may utilize multiple hinges, a tip aileron was pivoted on a shaft, where torque loading and flex became an issue. Finally, when connected via direct linkage, researchers observed that control loads felt at the yoke were often up to 3 times heavier than for conventional ailerons.
Here is an article by Bob Whittier explaining more.

What I meant by all-flying aileron was a control surface like a stabilator, but on the wing tip instead of the tail.

@BobMcGeoff When you said that you didn’t have much experience in aviation, I thought it best  from a more basic place. Since you clearly have some familiarity and have clarified your question, I’m happy to append my answer above.

Cody's design was based loosely on the Wrights'. However he did not buy into their demand for instability and raised the pitch of the foreplane accordingly. Besides his ailerons he also included a "top rudder" which augmented the net control authority in roll. Its flying characteristics deliberately made it a completely different aeroplane from the Wright's.

@BobMcGeoff: You should edit your question with that more specific description, if you want answers to it specifically.

Most early ailerons were all-flying surfaces fitted between the wing tips. Examples include the 1906 Santos-Dumont 14.bis, the first plane to fly in Europe, S.F. Cody's 1908 British Army Aeroplane No.1 and the Gold Bug, modified by Glenn Curtiss from his June Bug in 1909. Until then most if not all other types used wing warping or nothing. The hinged trailing-edge aileron made its appearance around this time on types such as the Farman and Dunne. Both warping and all-flying surfaces were soon consigned to history.
G.T.R. Hill revived the idea in the 1920s and early 30s with his Pterodactyl series of tailless aircraft. Several of these had all-flying wing tips which, like the Dunnes which had inspired him, acted as both aileron and elevator. As late as the 1950s he used them on the Short SB.4 Sherpa tailless aeroisoclinic wing prototype. Others such as Alexander Lippisch also tried them but offhand I cannot recall any that went into production.
Another variation, which has been revisited from time to time, mounts each aileron on a pair of trailing booms behind the wing tip. Otto Kauba evolved a series of Skoda-Kauba designs during WWII, I cannot recall the others off hand.
Overall they are not a good idea. Hinged ailerons are far easier to mount rigidly, so all-flying ones come with a weight penalty. Moreover a hinged aileron affects much of the wing in front of it, magnifying its control effect without increasing drag. Of course that means in practice that the hinged aileron can be made smaller and produce less drag.
All-flying tip ailerons have the advantage of maintaining control up to and beyond the stalling point of the main wing. But in practice maintaining pitch control is far the more important and it is generally easier to fit an all-flying tail.

This is good stuff @Guy Inchbald.

Some radio control gliders for the slope use each wing as an aileron. There are two basic types: wingerons have an elevator (so wings only need to act as ailerons), pitcherons have a fixed elevator and used the wings for both roll and pitch control. For pitcherons, each wing has to move independently of the other so the wings can rotate in opposite directions for roll control, and in sync for pitch control. The tranmitters have computers that take care of converting stick inputs into what is needed for roll and pitch control.
Example of a pitcheron model. This one has a fixed v-tail (no need for rudder on slope glider). The wind picks up at around 9:00 into the video.

Wingerons can do helicopter like spins (the image for the video is not the wingeron model). I set the video begin time to the start of the video clip of the wingeron model, which shows helicopter mode at the start and end of the video clip of that model.

Wing warping is what you are looking for, where the entire wing twists. The Wright Flyer and many early designs were wing warp designs, but they didn't persist because of the structural issues. In a wing warp design structural members have to bend, which can lead to fatigue and structural failure.

Not to mention spiralling forces on the pilot's controls as speed increases beyond 30 mph (50 kph) or so. Those at the time used to say that once a wing-warping plane got up to any speed, the plane controlled the pilot.

"can lead to fatigue and structural failure"  Will lead to fatigue and structural failure.


text:
Why don't we place the engine in the front of the wings?
I learnt in class today that fast-moving air over the wing of the plane, which causes a difference in pressure on the airfoil due to something called Bernoulli's principle.
If this is so why cant the engine be placed in front of the wings since the exhaust from the engine can help the plane in take off.
I'm only a beginner at fluid dynamics thus the silly question.

Most airplanes DO place the engine(s) in front of the wings.  E.g. all non-pusher single engine propellor planes, most twins, a lot of multi-engine prop planes...  With commercial jets, I suspect the main reasons for placing the engines in pods under the wing for lighter structure and ease of maintenance.

They can be, as on the An-72/74, which has the engines mounted above and forward of the wings in part to increase lift, utilizing the Coandă effect.
One downside is that this makes access for maintenance more difficult, which is a large factor in operation costs.
https://en.wikipedia.org/wiki/Antonov_An-72
https://en.wikipedia.org/wiki/Coand%C4%83_effect

The civilian version is the AN-74

In addition to the Antonov 72/74's, Boeing worked on the YC-14 concept as a replacement for the C-130's.

Also, many seaplanes have to place the engines as far up as possible, to keep the engines and propellers out of seaspray. This has the secondary effect of accelerating airflow over the wing and increasing its effectiveness.

The engine wash is also used to increase the effectiveness of control surfaces, an example for this is the A-10. The A-10 blows jetwash between the rudders and above the horizontal stabilizer, augmenting the efficiency of all these surfaces.

The downside is that the surfaces in contact with jetwash need to be designed to handle the soot and extra heat. The airplane also needs to be able to handle the lift imbalance in case of an engine failure.

Not a great example, but good to illustrate I think.

Positioning of the engine can severely affect the aircraft's CoP and CoG, having it directly at wing level must move CoP or CoG in abrupt ways.
Also, if an aircraft engine were to be creating fluctuations of exhaust gas, then the lift of the aircraft will also fluctuate.
Throttle of the engine would not only affect how much thrust the aircraft produces, but also how much lift it is using. If you wanted the aircraft to go faster but not gain any altitude, you would now need to pitch the aircraft's nose further down since a high amount of exhaust gas is being blown into the wings that is essentially adding to the aircraft's relative airflow and (if any) headwind. If a lot of lift is being produced, that is beyond the maximum deflection of the elevator, you may have some trouble maintaining altitude. To combat this, you could use flaps and spoilers, but these shouldn't be used at high airpseed in the first place.
The pilot also has to account for more factors. He/she must now also account for the additional lift that the aircraft's exhaust is providing for the aircraft.


text:
To be considered airworthy, are commercial aircraft fuselages required to support some amount of external overpressure without buckling?
I was thinking about whether an aircraft is designed to use internal pressure to maintain its rigidity (like some rockets) and then realized that this would probably be a bad idea because then a loss of pressure could be catastrophic. So, aircraft must be able to prove that they can fly when the difference between the inside and outside pressure is as low as zero. But then I started wondering if there might be a good reason why aircraft need to support a negative minimum pressure difference. For example, if the cabin pressure were, for some reason, equalized with ambient at a high altitude, and then the aircraft descended to sea level without re-equalizing pressure, the aircraft would experience a negative pressure difference. Another possibility is that there is a way for a hull breach in a worst-case location to combine with the airflow rushing past the aircraft to suck the air out of the cabin in a way that creates a negative pressure difference.
If either scenario is considered "possible", then perhaps commercial aircraft must be designed and tested to withstand negative pressure differences.
My question is:
a) Are commercial aircraft designed and tested to withstand negative pressure differences, and
b) If yes, how much negative pressure difference are they required to support?
Note: This question, which discusses pressure relief valves, provides a clue but does not clarify what negative pressure differential an aircraft cabin must actually be able to withstand.

One of the answers certainly answers part (a) provides a clue to part (b). Since the negative pressure relief valve opens at -1 psi, I assume that aircraft must be tested to at least -1 psi negative differential. But it's not a direct answer to part (b) of the question.

The certification specifications for large aeroplanes (CS-25) require that pressurized compartments can withstand differential pressure in either direction up to the relief valve setting:

For aeroplanes with one or more pressurised compartments the following apply:
(a) The aeroplane structure must be strong enough to withstand the flight loads combined with pressure differential loads from zero up to the maximum relief valve setting.
(b) The external pressure distribution in flight, and stress concentrations and fatigue effects must be accounted for.
(c) If landings may be made with the compartment pressurised, landing loads must be combined with pressure differential loads from zero up to the maximum allowed during landing.
(d) The aeroplane structure must be strong enough to withstand the pressure differential loads corresponding to the maximum relief valve setting multiplied by a factor of 1.33, omitting other loads. [...]

(EASA CS-25 - CS 25.365 Pressurised compartment loads, emphasis mine)
The relief valve setting can be different for each aircraft. Typically, the maximum positive pressure difference is much higher (since this is the normal case for pressurized aircraft) than the maximum negative pressure difference.
For example, on the Airbus A320 the limits are +8.6 psi and -1.0 psi respectively:

Two independent pneumatic safety valves prevent cabin pressure from going to high (8.6
psi above ambient) or too low (1 psi below ambient).
They are located on the rear pressure bulkhead, above the flotation line.

(Airbus A320 FCOM - Air Conditioning and Pressurization - Pressurization - Main Components - Safety Valves)
Compliance with the certification specification is not necessarily tested on the full aircraft, if other means are available:

Certification Approaches

The following certification approaches may be selected:
(a) Analysis, supported by new strength testing of the structure to limit and ultimate load. This is typically the case for New Structure.  [...]
(b) Analysis validated by previous test evidence and supported with additional limited testing. This is typically the case for Similar New Structure. [...]
(c) Analysis, supported by previous test evidence. This is typically the case for Derivative/ Similar Structure. [...]
(d) Test only.
Sometimes no reliable analytical method exists, and testing must be used to show compliance with the strength and deformation requirements. In other cases it may be elected to show compliance solely by tests even if there are acceptable analytical methods. In either case, testing by itself can be used to show compliance with the strength and deformation requirements of CS-25 Subpart C. In such cases, the test load conditions should be selected to assure all critical design loads are encompassed. [...]

(EASA CS-25 - CS 25.307 Proof of structure - AMC 25.307)

Wow - to test, do you vacuum/pressurize the interior, or, does there exist a sealed tunnel-like thing you can put the whole jumbo in and change the exterior pressure?!?!!

@Fattie I don't think they have a large enough vacuum chamber for that. You can do some tests on the ground with the outflow valve closed, but I guess some tests will have to be done in flight using manual pressurization control.

I see .. actually would it be necessary to do that in flight?  Wouldn't it be the same just sitting on the ground?

@Fattie the aircraft couldn't create a negative pressure difference (i.e. lower pressure inside the fuselage) by itself on the ground. It can in the air by maintaining cabin pressure while descending. Maybe they have some device to de-pressurize an aircraft on the ground, but I've never heard of it.

Gotchya, makes perfect sense.  I incorrectly assumed there was a "dial" ! and you could just set the interior pressure to any value reasonable value from slightly less than to slightly more than a bar - but I guess that is not the case

@Bianfable Not always true. The A320, for example, can create negative pressure due to avionics cooling extraction fans.

@Fattie It's easy to do it in flight. You close off the pressurization outflow valve then descend. In fact, it's possible to open the negative pressure valve during rapid emergency descents, particularly where the bleed air system/AC packs are inoperative.

@user71659 surely technically true but the cooling fans are surely not very powerful on that scale?!  Also, they duct to outside the aircraft?  How is that done, some sort of one way valve, pump ??

@Fattie Looking up the specs, its a 3 phase 115 V fan, 4200 W (5.6 HP), 509 liters/second. Yes, it's dumped overboard through a servo-controlled flap.


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Multiple annual inspections failed to find a problem that is now showing up - is there any recourse?
I purchased a 1977 Cessna 150M about 3 years ago. The aircraft is currently undergoing an annual inspection.
The inspector has determined that the engine serial number does not match the engine logbooks (and is therefore not airworthy). The aircraft has gone through many annual inspections. The report from the pre-purchase inspection I had performed clearly states "made sure all SN#'s match". Do I have any recourse? Am I just screwed?

you should see if Saavy Aviation will help you.

This sounds more like a legal question than an aviation one. What liability did the agreement with the pre-purchase inspector have? I'd seek the advice of a lawyer personally!

Per the other comment, you should email Mike Busch (Saavy) and ask him if there's a way for an AI to reconstruct a log from the other data like FAA records, or demonstrate that the mismatch is a writing error by somebody. Maybe you can find an AI who will do it for you. MIke is very good at responding to questions from aircraft owners.

I've got a note out to Savvy (coincendentially) I paid Savvy to manage the pre-buy inspection process.


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Are there regulations about carrying cargo on passenger seats?
We see that passenger aircraft have recently made cargo flights so that the supply chain does not decrease due to the Covid-19 crisis.
It is seen that the cargo boxes are loaded on the passenger seats by fastening them with a strap or rope.
https://twitter.com/AHoensbroech/status/1243095677485436928?s=09
Are there any regulatory restrictions (firefighting, smoke detection, aircraft weight&balance etc.) or guidance on carrying loads on the main deck of wide-body passenger aircrafts without removing the passenger seats (there will be no passengers on board)?

I removed the [pilots] tag because the question has nothing to do with it. Why did you add it again?

I want them to see that new concept and make the possible contribution. Would you stop editing my tags all the time?

I think you misunderstood what tags are for, see the tagging help page. Tagging [pilots] does not mean that pilots will be informed about this question or that they should answer it. It means that the question itself is about pilots, which this one isn't. Also, what do you mean by "all the time"? I edited once.

Thx for sharing the guide. I care about the answer to this question so i don’t want to leave more comments.


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How to choose the right map projections for flight plan?
There are 2 projection of maps that I saw online. UK CAA is a transverse projection map, while ICAO maps are conical.
It seems that transverse map is easier for flight planing as straight lines are rhumb lines, on the other hand the shortest route between two point is the great circle which is curved. So it's easy to calculate a heading, but it will not be the best route.
In conical map the straight lines are the Great circles so the best route, but its harder to calculate heading for flight.
What should be chosen and why? I didn't found info about the in the Internet...

Over what distance? Long flights this may make a difference, but for a couple hundred miles it may not be worth it. Typically winds aloft will have more effect

It all depends on how long is your path and if it includes polar regions or not. This is typically a question for GIS.

If it's the transverse Mercator projection, rhumb lines are NOT straight. They are in the Mercator projection. I don't know of any conic projections that have straight great circle lines between any 2 points. Maybe it's a gnomonic projection?

Are you planning on dead reckoning the whole way? Or will you (if the flight is long enough to warrant it) look at the great circle route and then pick some nav aids along that route for your actual flight plan?

@mkennedy: "Maybe it's a gnomonic", yes and why.

@mins Gnomonic displays great circle paths as straight lines. Other common azimuthal/planar projections like stereographic and azimuthal equidistant don't except if they're centered at a pole and the line passes through or ends at the pole.


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Does the DA-42 automatically lean to clean fouled spark plugs?
The DA-42 has an automatic run-up method. Specifically, the pilot in command is to hold two buttons (one for each engine) until the run-up is complete. Since the DA-42 has no manual mixture control, does it also automatically lean the mixture when foul spark plugs are detected?

It doesn't have spark plugs.

Depends on the variant.  Most DA-42s are powered by turbocharged Diesel engines and do not have spark plugs.  And yes the DA-42 uses an automatic run up cycle in order to test the Engine Control Units (ECU).  The test button is depressed and held while the automatic ECU cycle runs on both ECUs for each engine; the pilot simply monitors the engine gauges for signs of abnormalities.
Now the DA-42L is an exception to this rule as it is powered by Lycoming IO-360 gasoline engines.  It makes use of more conventional run-up procedures.


text:
Why would an airplane be approved for ditching?
So, the Learjet 60 that I used to fly has the following limitation:

My question, is why would a manufacturer certify an airplane for ditching if it isn't required?  The airplane is most likely going to be totaled anyway, right?
Or does it just mean that since it isn't certified for ditching that we aren't allowed to do it?  Guess no double engine failures over water will be in my near future....

This doesn't directly relate to the question, but the A-320 that Sully ditched in the Hudson River had a "ditching switch". Flipping this switch closes all through-hull fittings to make the plane less likely to flood and sink - of course structural damage or even open doors and windows can sink the plane quickly. But the ditching switch is intended to give the crew and passengers more time after splashdown. NB Sully and Skiles forgot about this switch and ditched successfully with the switch not activated, so it just helps in the landing but - as demonstrated - it is possible to survive the di

I think that 14 CFR 25.801 might sum this one up. Aircraft that are approved for ditching under 25.801 have to meet several requirements:

(b) Each practicable design measure, compatible with the general characteristics of the airplane, must be taken to minimize the probability that in an emergency landing on water, the behavior of the airplane would cause immediate injury to the occupants or would make it impossible for them to escape.
(c) The probable behavior of the airplane in a water landing must be investigated by model tests [emphasis mine] or by comparison with airplanes of similar configuration for which the ditching characteristics are known. Scoops, flaps, projections, and any other factor likely to affect the hydrodynamic characteristics of the airplane, must be considered.
(d) It must be shown that, under reasonably probable water conditions, the flotation time and trim of the airplane will allow the occupants to leave the airplane and enter the liferafts required by § 25.1415. [emphasis mine] If compliance with this provision is shown by buoyancy and trim computations, appropriate allowances must be made for probable structural damage and leakage. If the airplane has fuel tanks (with fuel jettisoning provisions) that can reasonably be expected to withstand a ditching without leakage, the jettisonable volume of fuel may be considered as buoyancy volume.
(e) Unless the effects of the collapse of external doors and windows are accounted for in the investigation of the probable behavior of the airplane in a water landing (as prescribed in paragraphs (c) and (d) of this section), the external doors and windows must be designed to withstand the probable maximum local pressures.

Basically, the aircraft needs to have its hydrodynamic behavior while ditching investigated, and it must then float long enough for the occupants to escape. It sounds like the Learjet 60, if ditched, is not guaranteed to either a) remain structurally sound, or b) allow the crew and passengers to get out before it slips below the waves.
An aircraft that was certified for ditching, on the other hand, basically means two things:

The crew knows that they have at least a chance of doing it right (and will possibly change how the aircraft is configured or prepared), probably with an actual published checklist available to them; and:
If the crew screws it up, it's their own fault and the manufacturer might not be held liable; the aircraft met certification standards. This would significantly reduce their liability in a crash. It's probably mostly that one, honestly.

Nice and correct answer. It's a legal thing and something the crew of cause should have in mind for decision making but if they are in an emergency and they still consider it to be the safest way to ditch,  this limitation should not be the reason why they crash attempting to avoid the ditching.

The main gist of my question is why would one jet be certified for it and another not?  If it isn't required, I'm honestly surprised that any of them do it based on how the aviation industry normally does these things.  What benefit does the manufacturer gain by certifying an airplane for ditching?

Airliners conducting extended overwater operations have to be certified for ditching.

@xpda It may have something to do with this.  I doubt that too many people will be doing atlantic crossings in the Lear!

@Lnafziger - What about island hops in the Caribbean or south pacific?

@chad well, technically you can be required to ditch in a pond, but with the reliability of modern turbine engines, the likelihood of having dual engine failures when you are relatively close to land is pretty slim.  The further you are from land though, the more likely you are to lose the second one in the time that it takes to reach land.

@Chad there are various requirements to be met that determine how far from land you can be.  The EMB-145 I flew could only do 50 nm offshore (no life rafts among other things), but we still serviced the Bahamas.  You just had to plan a route that kept you legal.  Same way we serviced the Yucatan in Mexico, by taking the long way around the Gulf of Mexico to get there.


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Why would an airplane pilot choose to intentionally use more runway than required for a takeoff?
An assumed temperature takeoff intentionally requires a pilot to use more runway than would be normally required.  Why would someone want to do that instead of getting off the runway in the minimum distance possible?

Relevant article: http://www.skybrary.aero/index.php/Reduced_Thrust_Takeoff#Assumed_Temperature but I'll leave an actual answer to someone with jet experience :)

An assumed temperature takeoff (also known as "flex" on Airbus/Fokker aircraft) is where the engine thrust is reduced to match the performance on a higher-temperature day, up to either the maximum thrust reduction allowed or the maximum assumed temperature that meets takeoff distance requirements. Unlike a derate, assumed temperature takeoffs do not reduce the minimum control speed used for calculating takeoff speeds ($V_{MCG}$ for $V_1$, $V_{MCA}$ for $V_2$).
The minimum selectable temperature is the lowest temperature beyond the flat rating temperature range (the range of temperatures where maximum thrust is achievable, limited by an engine control unit), and the highest temperature is the temperature at which the maximum thrust reduction allowed will be met. Except with specific certification and approval (such as 40% flex on the A340), such a procedure must not reduce the thrust beyond 25% of the nominal takeoff thrust (either full rate or a takeoff derate). For example, the range of assumed temperatures permitted is 30-75°C (flat rated to $ISA+15$, thrust at 75°C is 75% of normal rating).
The main reason for performing an assumed temperature takeoff is to conserve engine life, therefore reducing maintenance costs. According to Boeing, engine wear exponentially increases with the takeoff thrust used -- with engines costing about 10 million USD each, this has the potential to save a lot of money for airlines.
If you are taking off using assumed temperature, you may (but are not required to) add thrust to TOGA in the case of an emergency, however if you are using a takeoff derate, you must not increase the thrust beyond the derated N1, as this could cause a loss of control (higher thrust = higher actual $V_{MCG}$).
Not all aircraft allow assumed temperature in conjunction with derates. For example, you can only select a derate or a flex temperature on all Airbus aircraft (if a derate option is offered).
NOTE: do not attempt to "copy the jet jocks" in a piston aircraft and attempt a reduced throttle takeoff: only at takeoff throttle levels is extra fuel injected for cooling and reduction beyond this point could result in CHT levels rising to unacceptable levels, increasing the risk of engine damage.

It seems that engine wear decreases with longer runways. Are there ways for airliners to invest in longer runways?

Imagine you're doing a takeoff at a high density altitude. You need more runway to get up to speed because your engine is producing less power and you need to move faster to move the same amount of air over your wings as you would at a lower DA.
Aircraft can pretend the DA is higher by using a higher than normal temperature when calculating takeoff information. In jets with automated engine controllers, this setting -in a round about way- allows you to set the engines to produce only the minimum thrust required to get off the ground safely. Since that results in less thrust, there is less wear on the engine and that adds up significantly over time.
Your trade-off for this decreased wear is that you need more runway, which is usually readily available. If you suddenly need full power you just move the throttle to the Take-Off/Go-Around (TOGA) or emergency power setting (or push a TOGA button on the throttle), which overrides the temperature preset.

Very good answer, wish we could accept more than one!

If runway "is usually readily available" then the aircraft has spent too much time taxiing to the end of the runway.

It's basically a question of economics. Derating your takeoff means using a lower thrust setting for the engine which means less wear and thus less money spent on maintenance.

Economics for whom? That extra time of taxiing costs a lot to the passengers. I also imagine that loss of time for the airliners also costs a lot.

@DavidJonsson: What extra taxiing time?  You're still going to be starting from the same place, just rotating and lifting off further down the runway.

I refer to techniques to lessen the time from gate to the runway in order to minimize total travelling time for the passenger. Do people mean that any lengthening of the runway will be used as a longer lift off time to save engine wear?

Airshow pilots will sometimes use more runway than necessary.  They'll get the wheels off the ground but remain in ground effect (sometimes only a foot off the runway, which I count as "still using the runway") while accelerating.  The extra speed will permit them to make a dramatic vertical climb that's a lot steeper than Vy or Vx would permit.

Good point, but my question is about assumed temperature takeoffs!  :-)


text:
What can be expected in an airline interview?
So after the long wait, when someone finally gets that phone call for an interview at an airline, what do they need to study?  What kinds of questions will they ask during the interview?  How many interviews do they typically have to go through before a hire decision is made?  In short, how does it work?

The Delta Interview Process
I interviewed about three months ago at one of the several regionals that uses the Delta interview process.  It goes a little something like this:
Company Introduction
You arrive in the morning, somebody meets you, shakes your hand, and you usually hear a little speech or presentation about the company.  If your prospective employer uses AirlineApps, they'll have you verify that all of your information is still current, and gather your paperwork.  Then, it's off to Computer-Based Testing!

Computer Based Testing
CBT in the Delta interview is divided into three segments: cognitive, personality, and job knowledge.
Cognitive
The cognitive test is essentially reflex and memory games, of the sort you'd see on lumosity.com.  Some examples:

You are shown a horizontal line, with a pointer in the center.  The pointer will move from side to side at random along the line.  It is your task to counteract this random movement using the arrow keys to keep the pointer as close as possible to the center of the line.

Measures:  Focus and concentration

You are shown two words, such as DF3ET and DEFET.  It is your task to determine as quickly as possible if they are the same or different, and to click the appropriate same or different button on screen.

Measures: Attention to detail?

You are shown a table of six numerals paired with six simple shapes.  This table remains on screen.  You are shown a series of these shapes.  Decode, as quickly as possible, the series of shapes into the numerals they represent.

Measures:  Matching, working memory.

You are shown a graphic of a man holding a flag in one hand.  The man is either facing towards or away from you.  The man is either right-side-up or upside-down.  No matter his orientation, determine as quickly as possible whether the man is holding the flag in his right or left hand.

Measures:  Spatial awareness

A line wavers back and forth in a white area between two red zones in a random fashion.  When the space bar is pressed, the line will instantly be reset to the center of the white area.  It is your task to press the space bar as quickly as possible after the red line leaves the white area, but not before.

Measures:  Attention, reflexes.

You are shown the horizontal line with the pointer as well as the white area with the line.  It is your task to keep the pointer centered with the arrow keys while simultaneously using the space bar to reset the line when and only when it moves outside the white area.

Measures:  Division of attention, reflexes

You are shown a series of six simple shapes.  It is your task to recall the six numerals that were paired with these shapes from earlier in the test.

Measures:  Recall

A series of simple mental math problems is presented.  "Which would you rather have, 1/4th of \$200, 1/5th of \$300, or 1/3 of \$250?"

Measures:  Mental math skills

You are shown four rectangles.  One has a thin border, one contains a filled in arrow pointing left, one has a shaded arrow pointing right, one has a thick border.  There are multiple exercises to the test.  During some portions of the test, you are asked to click the rectangle whose arrow matches the direction of the one you are shown.  In others, you are asked to click the one whose shading matches.  In others, the border.  These criteria change at random.  Your task is to match the proper criteria as quickly and accurately as possible.

Measures:  Attention to detail, adaptation to changing conditions.

Listen through your headphones.  A series of notes will be played.  Then a second series of notes will be played.  Touch SAME or DIFFERENT.

Measures:  Whether you were good at Simon as a kid.

Personality
You are shown approximately 130 statements, one at a time.  Your task is to determine how much you agree or disagree with them on the following scale:

Strongly Agree
Agree
Neither agree nor disagree
Disagree
Strongly disagree

The statements are similar to:

I think the new morality is no morality at all.
Over the years, I have done some pretty stupid things.
I have literally jumped for joy.
I have a hard time resisting temptation.

Job Knowledge
This test measures technical knowledge.  It contains questions concerning:

Turbine engine theory
Descent planning
DME arc degree-to-nautical-mile calculations
Stall recovery procedures
Mach-to-TAS conversion
Transport category systems knowledge
Emergency procedures
Aerodynamics
and more!

Thank Wright that's out of the way, next up is lunch!
Then comes the interviews:

Tell me about a scary time in the cockpit
What would you do if you were an FO and the captain arrived smelling like alcohol?
Which is colder, -40 C or -40 F?
I see that you failed a checkride, tell me about it.

And so on.

The conclusion
You made it!  Someone comes out and shakes your hand.  Now it's time to fill out PRIA paperwork and pee in a cup.  If all goes well, you're given a conditional offer of employment!  Congrats!  You're a regional FO!
(If you can make it through training)

Wow...that sounds like a horrible interview process.

I always loved the -40 question. And I don't think I've ever even heard of an interview where the alcohol-smelling captain question wasn't asked in some variation. My favorite was always the "You're on final and the Captain is the Flying Pilot. You notice that he strongly smells like alcohol. What do you do?" That one gets a bit more into the safety of the aircraft rather than if you'd stand up to the Captain. And there's always "The Captain is Flying Pilot and you're on final. The Captain becomes unresponsive. What do you do?"